Together we sync: a systematic qualitative and quantitative review of fMRI hyperscanning studies

Social interaction relies on neurocognitive processes that support mutual prediction and coordination. Traditional neuroimaging investigates brain activity at the individual level, limiting insight into the reciprocal nature of social exchange. Hyperscanning overcomes this by simultaneously recording brain activity from interacting individuals. We conducted a systematic review of 28 functional magnetic resonance imaging (fMRI) hyperscanning studies examining inter-brain coupling during interactive tasks. We assessed study features and examined whether paradigms included four key properties that make the use of hyperscanning particularly valuable over single-brain designs: real-time reciprocity, mutual information flow, unpredictability, and irreproducibility. Substantial methodological heterogeneity was observed, and only a few studies incorporated all four theoretically relevant features. To identify consistent spatial neural patterns of inter-brain coupling, we performed coordinate-based hierarchical clustering on residual (task-independent) and task-evoked coupling data. The latter was further analysed in relation to the complexity of the interaction. Residual coupling consistently involved the right posterior superior temporal gyrus, overlapping with the anterior temporo-parietal junction (TPJ), suggesting a role in spontaneous alignment. Task-evoked coupling differed by interactional complexity, with posterior temporal regions involved in low-complexity tasks, and medial frontal, mid-cingulate, and insular areas in high-complexity ones. These findings support the relevance of fMRI hyperscanning for studying inter-brain dynamics and inform future methodological development.